A driver's view of the Dorsett Road diverging diamond interchange looking west

What is a diverging diamond interchange?

The diverging diamond interchange (DDI) is a new type of interchange traffic solution. The nation's first diverging diamond interchange was completed in 2009 in Springfield, Missouri. MoDOT has since built a second diverging diamond interchange at National Avenue/James River Freeway (Route 60).

MoDOT's third DDI was completed October 17, 2010 in St. Louis, at the Interstate 270 and Dorsett Road interchange.

The diverging diamond interchange has been used in France. The Federal Highway Administration has been advocating innovative intersection designs as a way to increase capacity, decrease congestion and minimize the cost of new infrastructure.

How does the DDI work?

The diverging diamond interchange allows free left turns for motorists, meaning vehicles don’t cross opposing traffic. Traffic models indicate this type of interchange works well with areas of heavy traffic.

Examples of how the DDI works can be seen in the following animation below. The YouTube video link gives drivers an idea of what it's like to navigate the diverging diamond interchange currently under construction at the Interstate 270 and Dorsett interchange.

Because the DDI does not have any left turns that must clear opposing traffic, the design can improve traffic movement with more green time. It will move traffic faster, reduce congestion, and increase safety.

With the help of public input by citizens of Maryland Heights, MoDOT has chosen the diverging diamond interchange option for the intersection of Interstate 270 and Dorsett Road. The DDI will help with current heavy traffic volumes. It is also less costly to build than conventional diamond interchanges.